Linear regenerator with circulating heat transfer surface

ABSTRACT

A regenerative heat exchanger for transferring heat from the exhaust gas to the intake working fluid of a prime mover and from the pressurized working fluid to the exhaust vapor of a heat pump. Application is especially useful in a system in which liquid air or nitrogen made by a heat pump provides compression cooling for a gas turbine prime mover. The heat exchanger employs circulating element heat transfer surface such as wire belts or ceramic balls, which circulate in turn through working fluid exhaust and intake channels while absorbing and rejecting heat between the two channels. Effectiveness exceeding 98% increases thermal efficiency of small low-pressure ratio gas turbines.

REFERENCES

-   1.) Kaufman, Jay S., U.S. Pat. No. 7,398,841 B2, Jul. 15, 2008 -   2.) Kaufman, Jay S., U.S. patent application Ser. No. 12/315,002,     Nov. 26, 2008

BACKGROUND OF THE INVENTION

The present invention relates to regenerative heat exchangers for heat recovery in prime movers, heat pumps and other mechanical equipment for vehicle and stationary use and pertains particularly to an improved regenerator for gas turbine engines and gas liquefiers. References 1 and 2 describe a gas turbine with refrigerated compression by a liquefied or solidifed gas for increasing thermal efficiency of the engine. The regenerator of the present invention is designed to minimize the refrigerant requirement by decreasing regenerator terminal temperature difference relative to turbine expansion temperature drop, thereby increasing the ratio of compressed air to refrigerant. Similarly, reduction of terminal temperature difference of a heat pump regenerator increases specific yield of the heat pump supplying refrigerant to the gas turbine. In addition, high effectiveness of the regenerator of the present invention acts to increase thermal efficiency of conventional gas turbines with ambient air compression.

The regenerator of the present invention employs circulating elements, such as a continuous belt or non-connected ceramic balls, which circulate in the upstream direction to absorb heat from the lower pressure exhaust side and reject heat to the pressurized side of the regenerator. The material of the circulating elements has high thermal storage capacity and conductivity. Heat duty of the regenerator is matched to the heat transfer rate from the low to high pressure side by adjusting speed of the circulating elements, providing effectiveness of up to 98% with minimal differential temperature between the working fluid and circulating elements. The belt type element is supported on pulleys at each end of the regenerator and passes through seals having minimal leakage area between the working fluid and surrounding atmosphere. Ball type elements are similarly sealed, and are guided while immersed in the working fluid in the exhaust flow channel of the regenerator. The ball type configuration is adaptable to very high temperature applications using ceramic components.

Current practice for most gas turbines utilizing heat recovery to increase thermal efficiency is to employ recuperators with fixed surface area. Because of surface area constraints, especially in motor vehicle application, terminal temperature difference of counter-flow recuperators is excessive and the resulting low effectiveness reduces gas turbine efficiency. The majority of these recuperators are constructed of numerous tubes, brazed or welded in complex header arrangements. More advanced state-of-the-art stationary recuperators rely upon laminar flow of the working fluid in a plate type matrix with numerous parallel flow passages to realize acceptable effectiveness. Both types of recuperators are expensive, especially with high temperature alloys, because of the large number of closely spaced joints. Another kind of heat exchanger in use is the rotary regenerator which attains higher effectiveness than recuperators by providing passage of the low and high pressure flow streams over the same heat transfer surface. Parallel passage seals are required to minimize leakage from the high to low pressure side and application is limited to moderately pressurized systems. Rotary regenerators also require numerous parallel flow passages with closely spaced brazing or welding. In addition, metal recuperators and rotary regenerators are limited to inlet gas temperature of about 1000 K (1800 R).

Another application of heat exchangers with fixed surface area is for cooling compressed working fluid prior to two-phase expansion in heat pumps. There is also a need to improve effectiveness and simplify construction of these heat exchangers for liquefiers and solidifiers.

The regenerator of the present invention provides variable heat transfer surface area dependent on speed of the circulating belt or other circulating elements to increase effectiveness. Another feature of the regenerator of the present invention is replacement of the multiple parallel heat transfer circuits by an upstream and a downstream channel connected in series to a prime mover or heat pump. As a result it is only necessary to seal the relatively small cross sectional area of the heat transfer elements against the pressure differential between working fluid and atmosphere. Fabrication is simplified by elimination of brazed and welded tube and plate construction, which also reduces working fluid pressure loss. Energy input required to drive the heat transfer elements is negligible. Circulation speed of belts or balls is determined by their configuration including material, quantity and surface area in addition to working fluid flow parameters. Effective heat transfer area of the circulating belt is less than 10% as compared to a fixed area heat exchanger of the same heat duty. In addition, high effectiveness improves the potential for low temperature heat addition from recovered heat in sub-ambient prime mover application. Available heat sources include overcast solar, building exhaust and vehicle drive train energy loss.

SUMMARY AND OBJECTS OF THE INVENTION

It is the primary object of the present invention to provide an improved regenerator for increasing thermal efficiency of prime movers and other mechanical equipment. In accordance with a primary aspect of the present invention, a linear regenerator for recovering heat in prime movers and other mechanical equipment comprises a two-channel assembly and a circulating element assembly. The two-channel assembly directs the flow of working fluid in a pressurized channel from an air pressurizer such as a compressor or fan to a working fluid heater such as a combustor or solar absorber and in an exhaust channel from a discharge port of a prime mover to atmosphere. The circulating element assembly transfers heat from the exhaust channel wherein heat is absorbed by the elements to the pressurized channel wherein heat is rejected from the elements. The two-channel assembly comprises a support structure for holding the channels in spaced relation while maintaining position of working fluid connections between the regenerator and the pressurizer, air heater and prime mover. In addition the two-channel assembly comprises insulation for minimizing heat loss from the channels to atmosphere, and seals for minimizing working fluid loss between the element to channel interface and atmosphere. The circulating element assembly with belt type elements comprises hot and cold end pulleys with bearings for guiding the heat transfer belt and an electric motor for driving the belt at a selected speed. Similarly, a circulating ball type assembly comprises one or more open conduits for guiding the heat transfer balls and a controllable feed mechanism with an electric motor for circulating the balls at a selected speed.

It is another object of the present invention to provide a regenerator constructed with ceramic components for use with prime movers and other mechanical equipment having very high working fluid gas temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the present invention will become apparent from the following description when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a front elevation section view illustrating a preferred embodiment of the circulating belt regenerator of the present invention for below ambient heat transfer as part of a gas turbine with refrigerant cooled compression.

FIG. 1A is a side elevation view of the regenerator of FIG. 1.

FIG. 2 is a front elevation section view illustrating a preferred embodiment of the circulating belt regenerator of the present invention for below ambient heat transfer as part of a heat pump.

FIG. 3 is a front elevation section view illustrating a preferred embodiment of the circulating belt regenerator of the present invention for below and above ambient heat transfer as part of a gas turbine with refrigerant cooled compression.

FIG. 4 is a front elevation section view illustrating a preferred embodiment of the circulating ball regenerator of the present invention for heat transfer above the upper temperature limit of a connected heat exchanger.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a front elevation section view illustrating a circulating belt regenerator 10 of the present invention with exemplary embodiments of a circulating wire belt assembly 12 and a two-channel assembly 14 for connection to gas turbine of a motor vehicle. An air intake channel 16 directs air working fluid 18 from atmosphere via an air intake nozzle 20 and a compressor intake nozzle 22 to a compressor 24 with cooling by liquid nitrogen 26. Simultaneously, a pressurized channel 28 directs working fluid from the compressor via a compressor discharge nozzle 30 and a heater nozzle 32 to a heater 34, connected in turn to a turbine 36 of the gas turbine. Heat addition to the heater is by re-circulated drive train transmission fluid 38. A hot box 40 and a cold box 42 close the ends of each channel, providing retention of belt seals 44, 46, 48 and 50. The seals minimize leakage of working fluid between a circulating wire belt 52 and the closed ends of each channel. The wire belt and seals are part of circulating belt assembly 12 which also includes a hot pulley, bearing and shaft assembly 54 supported by the hot box and a cold pulley, bearing and shaft assembly 56 supported by the cold box.

FIG. 1A is a side elevation view from FIG. 1 rotated ninety degrees to illustrate attachment of a belt drive motor 58 which drives the wire belt via the cold pulley, bearing and shaft assembly.

Performance of the regenerator is estimated for installation in a sub-compact vehicle. The gas turbine develops 6.7 kW (9 HP) at a cruising speed of 80 km/hr (50 mph) with a pressure ratio of 3 and turbine inlet gas temperature of 370 K (670 R). Heat addition is by recovery of motor vehicle drive train heat using re-circulated transmission fluid at 390 K (700 R). At these conditions regenerator inlet gas temperature from the turbine is 294 K (530 R), effectiveness is 98%, and belt speed is 8.7 m/min (29 ft/min), corresponding to 11 rpm for a channel length of 0.3 m (1 ft), during 1 hour of operation.

FIG. 2 is a front elevation section view illustrating a circulating belt regenerator 100 of the present invention with exemplary embodiments of a circulating wire belt assembly 112 and a two-channel assembly 114 for connection to a gas turbine. The configuration of regenerator 100 is similar to regenerator 10 of FIG. 1 with the addition of an over-ambient exhaust channel 117 and a longer pressurized channel 128. An air intake channel 116 directs air working fluid 118 from atmosphere via an air intake nozzle 120 and a compressor intake nozzle 122 to a compressor 124 with cooling by liquid nitrogen 126. Simultaneously, a pressurized channel 126 directs working fluid from the compressor via a compressor discharge nozzle 128 and a combustor nozzle 132 to a combustor 134, connected in turn to a turbine 136 of the gas turbine. Exhaust channel 117 directs exhaust working fluid from the turbine to atmosphere via a turbine nozzle 137 and an exhaust nozzle 139.

Performance of the regenerator is estimated for installation in a compact vehicle. The gas turbine develops 14 kW (19 HP) at a cruising speed of 105 km/hr (65 mph) with a pressure ratio of 3 and turbine inlet gas temperature of 1170 K (2100 R). Heat addition is by combustion of fuel. At these conditions regenerator inlet gas temperature is 944 K (1700 R), effectiveness is 98%, and belt speed is 7.6 m/min (25 ft/min) corresponding to 5 rpm for a channel length of 0.6 m (2 ft), during 1 hour of operation.

FIG. 3 is a front elevation section view illustrating a circulating ball regenerator 200 of the present invention with exemplary embodiments of a circulating ball assembly 212 and a two-channel assembly 214 for connection to an intermediate heat exchanger operating at a lower temperature. A pressurized working fluid channel 228 directs working fluid 218 from a pressurized outlet nozzle 219 of the intermediate heat exchanger via an intake nozzle 226 and a combustor nozzle 230 to the working fluid inlet of a gas turbine 236. Simultaneously, a low pressure channel 217 directs the working fluid from the turbine via a turbine nozzle 237 and an outlet nozzle 239 back to a low pressure inlet nozzle 221 of the intermediate heat exchanger. Ball seals 244 and 246 minimize leakage of working fluid between falling ceramic balls 252 and the closed ends of channel 228. The ceramic balls are part of the circulating ball assembly which includes a perforated ball guide 248 attached between a high temperature box 236 and an intermediate temperature box 242, a ball advance worm 256, and a worm gear drive motor 258. High temperature components are of ceramic materials, as required.

Performance of the ball regenerator is estimated for installation in an electric generating station. The gas turbine develops 300 kW (400 HP) continuously with a pressure ratio of 3 and turbine inlet gas temperature of 1670 K (3000 R). Heat addition is by combustion of fuel. At these conditions regenerator inlet gas temperature is K 1360 K (2440 R), effectiveness is 98%, and ball speed is 124 m/min (400 ft/min), corresponding to 160 rpm for a channel length of 0.3 m (1 ft), during 1 hour of operation.

FIG. 4 is a front elevation section view illustrating a circulating belt regenerator 300 of the present invention with exemplary embodiments of a circulating wire belt assembly 312 and a two-channel assembly 314 for connection to a gas liquefier. A pressurized channel 328 directs liquefier air working fluid 318 from atmosphere via a liquefier compressor 324, a compressor discharge nozzle 328 and an expander intake nozzle 330 of the liquefier to the intake of a turbo-expander 336. Simultaneously, an exhaust channel 317 directs the vapor portion of liquefier working fluid from a liquid-vapor separator 338 via a separator nozzle 337 and an exhaust nozzle 339 to atmosphere while the liquid portion 340 is drawn off to a Dewar 342.

Performance is estimated for a circulating belt regenerator of an air liquefier capable of supplying liquid air for compression cooling of the 300 kW (400 HP) gas turbine of FIG. 3. Wind energy drives the liquefier compressor. During air liquefaction, regenerator inlet gas temperature is 294 K (530 R), effectiveness is 97%, and belt speed is 6 m/min (20 ft/min), corresponding to 7.5 rpm for a channel length of 0.3 m (1 ft), during 1 hour of operation.

While I have illustrated and described my invention by means of specific embodiments, it is to be understood that numerous changes and modifications may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. For example, working fluid leakage may be stopped by injection of a purge flow downstream of the seals, the rate of heat transfer between working fluid and heat transfer elements may be enhanced by injection of a non-luminous gas into the channels, and prime mover heat input may include solar. 

1. A regenerative heat exchanger comprising movable heat conveyance means circulating generally parallel to the flow of the working fluid of a machine selected from the group consisting of prime movers and heat pumps, for transferring heat at generally less than ambient temperature, wherein exhaust heat of said prime mover heats prime mover working fluid flowing from liquefied or solidified gas cooled compression means of said prime mover to heat addition means of said prime mover, and wherein expansion cooled exhaust vapor of said heat pump cools heat pump working fluid flowing from compression means of said heat pump to expansion means of said heat pump.
 2. The heat exchanger of said prime mover of claim 1 comprising working fluid containment and channeling means including a prime mover exhaust channel connected between prime mover expansion means and prime mover exhaust means, and a pressurized prime mover channel connected between the discharge of said prime mover compression means and the intake of prime mover heat addition means.
 3. The heat conveyance means of claim 2 comprising a heat storage and transfer belt loop with belt loop circulation means for moving said belt loop, primarily immersed in said working fluid, between said pressurized working fluid in said pressurized prime mover channel and said exhaust working fluid in said prime mover exhaust channel.
 4. The belt loop of claim 3 wherein said belt loop comprises wire configured as a coiled extension spring for maintaining tension of said belt loop.
 5. The heat addition means of claim 1 comprising heat transfer means, wherein heat from a heat source external to said prime mover is absorbed by an intermediate fluid circulating through said heat addition means while an approximately equivalent quantity of said heat is transferred from said intermediate fluid to said prime mover working fluid in said heat addition means.
 6. The heat source of claim 5 wherein said intermediate fluid comprises drive train transmission fluid of a motor vehicle powered by said prime mover.
 7. The heat source of claim 6 wherein said intermediate fluid is heated by solar energy.
 8. The working fluid containment and channeling means of claim 2 comprising heat conveyance means for transferring heat above ambient temperature from exhaust working fluid of said prime mover to pressurized working fluid flowing from compression means of said prime mover to heat addition means of said prime mover.
 9. The heat conveyance means of claim 8 comprising a plurality of heat storage elements with circulation means to move said elements, primarily immersed in said working fluid, from said downstream channel to said upstream channel, wherein said elements absorb a quantity of heat from working fluid downstream of said expansion means while transferring an approximately equivalent quantity of said heat to said fluid at higher pressure upstream of said expansion means.
 10. The heat exchanger of claim 9 comprising seal means, wherein a purge flow of gas is injected downstream of working fluid leakage paths of said channeling means to retain said working fluid within said channels.
 11. The heat conveyance means of claim 9 wherein said elements are made of ceramic material.
 12. The heat conveyance means of claim 9 wherein said elements are spherical balls.
 13. The heat exchanger of claim 9 comprising gas injection means, wherein non-luminous gas is injected into said channels to increase the rate of radiation heat transfer between said working fluid and said heat conveyance means.
 14. The heat exchanger of said heat pump of claim 1 comprising working fluid containment and channeling means including a heat pump exhaust channel connected between heat pump expansion means and heat pump exhaust means, and a pressurized heat pump channel connected between the discharge of heat pump compression means and the intake of said heat pump expansion means.
 15. The heat conveyance means of claim 14 comprising a heat storage and transfer belt loop primarily immersed in said working fluid and belt rotation means for circulating said belt loop between said pressurized working fluid in said pressurized heat pump channel and said exhaust working fluid vapor in said heat pump exhaust channel.
 16. The belt loop of claim 15 wherein said belt loop comprises wire configured as a coiled extension spring for maintaining tension of said belt loop.
 17. The heat exchanger of claim 14 comprising seal means, wherein a purge flow of gas is injected downstream of working fluid leakage paths of said channeling means to retain said working fluid within said channels.
 18. A regenerative heat exchanger of a prime mover comprising movable heat conveyance means primarily immersed in both pressurized working fluid and lower pressure exhaust of said working fluid while circulating generally parallel to the flow of said fluid, for transferring exhaust heat of said working fluid to said working fluid flowing from compression means of said prime mover to heat addition means of said prime mover.
 19. The heat exchanger of claim 18 comprising at least: one intake channel in working fluid communication with an air compressor and a pressurized heater, one exhaust channel in working fluid communication with a gas turbine and atmosphere, and one circulating wire belt with belt drive means, wherein said belt absorbs heat from working fluid flowing in said exhaust channel while rejecting an approximately equivalent quantity of said heat to said working fluid flowing in said intake channel.
 20. A prime mover of a motor vehicle comprising a regenerative heat exchanger with a movable heat conveyance belt circulating generally parallel to the flow of the working fluid of said prime mover, and a working fluid heater, wherein said belt transfers heat at generally less than ambient temperature from exhaust heat of said prime mover to said working fluid flowing from a working fluid compressor of said prime mover to said heater, and wherein heat from transmission fluid of a drive train transmission of said vehicle increases the temperature of said working fluid in said heater. 